The basic theory and operation of thermoelectric devices has been developed for many years. Thermoelectric devices can function as either a cooler or a heater. Thermoelectric devices are essentially small heat pumps which follow the laws of thermodynamics in the same way as mechanical heat pumps, refrigerators, or any other apparatus used to transfer heat energy. The principal difference is that thermoelectric devices function with solid state electrical components as compared to more traditional mechanical/fluid heating and cooling components.
A circuit for a simple thermoelectric device generally includes two dissimilar materials such as N-type and P-type thermoelectric semiconductor elements. The thermoelectric elements are typically arranged in an alternating N-element and P-element configuration, and the thermoelectric elements are coupled electrically in series and thermally in parallel. The Peltier effect occurs when voltage is applied to the N-type and P-type elements resulting in current flow through the serial electrical connection and heat transfer across the N-type and P-type elements in the parallel thermal connection. In a typical thermoelectric element array, the direction of heat transfer is indicated by the direction of net current flow through the thermoelectric elements.
A disadvantage of currently available thermoelectric device circuits is their lack of fault tolerance. Because the thermoelectric elements are electrically connected in series, the failure of a single element generally causes an open circuit condition in the device. The open circuit prevents any of the elements in the thermoelectric device from receiving the current required to provide cooling or heating. Since a single failed element within currently available thermoelectric device circuits can cause the entire thermoelectric device to fail, presently available thermoelectric device circuits are said to lack fault tolerance.
Currently available thermoelectric device circuits also have the disadvantage of lacking fault notification. Cooling and heating stop when currently available thermoelectric device circuits fail, but no failure indication is provided. If the thermoelectric device circuit is not checked periodically, the load to which the thermoelectric device circuit is applied may be damaged.
Presently available thermoelectric device circuits are difficult, if not impossible, to troubleshoot and repair because they lack fault isolation. Thermoelectric device circuits may contain multiple thermoelectric elements and devices. It is a difficult task to identify a failed or intermittent element within a long series of elements without a fault isolation mechanism in the circuit.
Previously developed thermoelectric device circuits have low mean-time-between-failure (MTBF) ratings because the serial coupling of thermoelectric elements does not provide fault tolerance. Presently available thermoelectric device circuits may be, therefore, undesirable to use because they do not provide fault tolerance, fault notification, or fault isolation.